Rotary joints

ABSTRACT

Rotary joints are provided, for use in allowing fluid flow from a stationary member to a rotating joined member.

TECHNICAL FIELD

[0001] This invention relates to rotary joints, and more particularly torotary joints used with calendar rolls.

BACKGROUND

[0002] In the papermaking field, rotary joints are often used to deliverhot fluid, e.g., hot oil, to a rotating calendar roll to heat thesurface of the roll. Bearings, requiring a dedicated lubrication system,are generally used to support and separate the rotating and stationarycomponents of the joint. Mechanical seals are generally used to preventleakage of the fluid as it passes from a supply, through the rotaryjoint and into the calendar roll. These bearings and seals are subjectto failure, and in some cases failure of the rotary joint may result infire due to the presence of the hot oil.

[0003] Similar joints are used in the textile industry, for example, onlaminating rolls used in carpet manufacturing and press rolls inchipboard mills.

SUMMARY

[0004] The present invention features a rotary joint that provides goodsealing between a rotating member, such as a calendar, press, orlaminating roll, and a stationary member, such as a conduit forsupplying fluid to the rotating member. Sealing is provided without theuse of mechanical seals providing a safe, reliable seal. In preferredimplementations, the rotary joint is also free of any bearings. Sealingis provided by floating ring seals that can be easily assembled andmaintained. The floating rings allow relative movement between the partsthat are being sealed, accommodating thermal expansion and contractionof the parts and the radial movement of the rotating member due to thebearing radial internal clearance. In some implementations, the sealsare configured to allow a controlled amount of fluid to leak from apurged chamber of the rotary joint, and, if desired, this fluid isrecycled back into the rotary joint via a fluid loop. Preferred rotaryjoints provide enhanced safety in the manufacturing environment, and canbe used with hot, flammable fluids such as hot oil, with little or nodanger of fire.

[0005] In one aspect, the invention features a rotary joint configuredto couple a rotating member to a relatively stationary member, including(a) a housing, configured to fit over the rotating member and receive afluid to be delivered from the stationary member to the rotating member,(b) a rotatable coupling disposed within the housing, configured to befixedly attached to the rotating member, and (c) a floating seal systemconfigured to allow a controlled amount of fluid to leak from the rotaryjoint during delivery of a fluid from the stationary member to therotating member.

[0006] Some implementations may include one or more of the followingfeatures. The controlled amount is from about 0.5 to 2.0% of the totalflow of fluid into the rotary joint. The controlled amount is from about1 to 20 gallons/minute. The rotating member includes a calendar roll.The floating seal system includes a plurality of floating labyrinthseals. The floating labyrinth seals are disposed between the rotatablecoupling and portions of the housing. The rotary joint further includesa nitrogen-purged chamber configured to capture the fluid leaking fromthe rotary joint and allow this fluid to be collected for return to therotary joint. The rotary joint does not include bearings. The rotaryjoint does not include mechanical seals. The housing and rotatablecoupling are formed of the same material, e.g., steel. The floating sealsystem is configured to allow air to self-vent through the rotary jointupon start-up after a maintenance outage. The floating seal system isconfigured to allow air to vent through the rotary joint at a rate of atleast 25 gallons/minute, preferably at least 100 gallons/minute.

[0007] In another aspect, the invention features a rotary jointconfigured to couple a rotating member to a relatively stationarymember, including (a) a housing, configured to fit over the rotatingmember, (b) an end plate, extending from a distal end of the housing andconfigured to allow the stationary member to be fixedly attached to thehousing, (c) a rotatable coupling disposed within the housing,configured to be fixedly attached to the rotating member, and to receivea portion of the end plate in sealing engagement, (d) a first seal,configured to provide sealing engagement between the rotatable couplingand the portion of the end plate, and (e) a second seal, configured toprovide sealing engagement between the rotatable coupling and an innerwall of the housing.

[0008] Some implementations may include one or more of the followingfeatures. The joint further includes a third seal, configured to providesealing engagement between a rotatable roll journal and the inner wallof the housing. The first, second and third seals are floating seals,e.g., floating labyrinth seals. The rotary joint does not includebearings. The rotary joint does not include mechanical seals. Thehousing and rotatable coupling are formed of the same material, e.g.,steel. The first seal is a high-pressure seal. The second seal is alow-pressure seal. The third seal is a purge gas-conserving seal. Therotatable coupling includes a second portion configured for insertioninto a cavity in the rotating member. The stationary member isconfigured to deliver a fluid to the rotating member through the rotaryjoint. The second portion of the rotatable coupling sealingly engagesthe portion of the end plate, the sealing engagement being provided bythe first seal. The second portion of the rotatable coupling and theportion of the end plate define a bore. The end plate defines an inlet,and the bore is configured to allow fluid flow from the inlet to acavity in the rotating member. The end plate further defines an outlet,and an outer wall of the second portion of the rotatable coupling and aninner wall of a cavity in the housing define a passage through whichfluid can flow from the rotating member to the outlet.

[0009] In yet a further aspect, the invention features a method ofdelivering fluid from a stationary source to a rotating member,including (a) delivering a fluid from the source to a rotary jointcomprising a housing, configured to fit over the rotating member andhaving a portion configured to receive the fluid, (b) passing fluidthrough a rotatable coupling, disposed within the housing and configuredto be fixedly attached to the rotating member, and (c) allowing acontrolled amount of fluid to leak past a floating seal system disposedbetween the rotatable coupling and the housing.

[0010] Some implementations may include one or more of the followingfeatures. The controlled amount is from about 0.5 to 2.0% of the totalflow of liquid into the rotary joint. The controlled amount is fromabout 1 to 20 gallons/minute. The floating seal system includes aplurality of floating labyrinth seals. The method further includescollecting the leaked fluid and returning it to the source for deliveryinto the rotary joint. The liquid is hot oil, e.g., mineral oil. Themethod further includes purging air-containing areas of the housing,e.g., purging them with an inert gas to inhibit oxidation of the oil.The liquid has a viscosity lower than that of water when the liquid isbeing circulated near its fluid maximum bulk operating temperature.

[0011] In another aspect, the invention features a floating seal forsealing between an inner cylindrical surface and an outer cylindricalsurface, the inner and outer surfaces defining a chamber. The sealincludes (a) a plurality of rings configured to fit in the chamber,positioned side-by-side along the length of the chamber, and to floatwithin the chamber, and (b) a biasing member configured to apply anaxial end pressure to the rings in the direction of fluid entering thechamber during use of the seal, keeping the rings compressed togetherand against an end face of the chamber to minimize leakage around theoutside diameter of the rings.

[0012] Some implementations may include one or more of the followingfeatures. The chamber that contains the rings is at least 0.100 inchlarger in diameter than the outer diameter of the rings, e.g., thechamber is from 0.100 to 1.00 inch larger in diameter than the outerdiameter of the rings. The biasing member includes a wave spring. Thefloating seal is configured to minimize leakage of a liquid through theseal. The rings are configured to provide a tortuous path comprisingalternating restricted areas and larger turbulence-creating void areas.

[0013] The invention also features, in another aspect, a floating sealfor sealing between an inner cylindrical surface and an outercylindrical surface, the inner and outer surfaces defining a chamber,the seal including a plurality of rings configured to define a tortuouspath comprising alternating restricted areas and largerturbulence-creating void areas.

[0014] In another aspect, the invention features a rotary jointconfigured to couple a rotating member to a relatively stationarymember, including (a) a housing, configured to fit over the rotatingmember and receive a fluid to be delivered from the stationary member tothe rotating member, (b) a rotatable coupling disposed within thehousing, configured to be fixedly attached to the rotating member, and(c) a floating seal system comprising a floating labyrinth sealincluding a plurality of rings configured to define a tortuous pathcomprising alternating restricted areas and larger turbulence-creatingvoid areas.

[0015] The term “floating seal”, as used herein, refers to a seal that,when sealingly disposed between two parts, allows clearance and relativeaxial and radial movement between the two parts.

[0016] The details of one or more embodiments of the invention are setforth in the accompanying drawings and the description below. Otherfeatures and advantages of the invention will be apparent from thedescription and drawings, and from the claims.

DESCRIPTION OF DRAWINGS

[0017]FIG. 1 is a perspective view of a rotary joint according to oneaspect of the invention.

[0018]FIG. 2 is an axial cross-sectional view of the assembly shown inFIG. 1.

[0019]FIG. 2A is an enlarged view of the area indicated in dotted linesin FIG. 2.

[0020]FIG. 2B is a view similar to FIG. 2A, with fluid indicated byshading.

[0021]FIG. 2C is a view similar to FIG. 2A, with rotating partsindicated by cross-hatching.

[0022]FIG. 3 is an enlarged detail view of a portion of FIG. 2A (asindicated by dotted lines in FIG. 2A), showing a floating sealconfiguration according to one embodiment of the invention.

[0023]FIG. 4 is an enlarged detail view of another portion of FIG. 2A(as indicated by dotted lines in FIG. 2A), showing a nitrogen-conservingfloating seal.

[0024]FIGS. 5 and 5A are, respectively, top and cross-sectional views ofa ring suitable for use in a floating seal. FIG. 5A is taken alongsection line 5A-5A in FIG. 5.

[0025]FIGS. 6 and 6A are, respectively, front and sectional views of awave spring suitable for use in a floating seal.

[0026] FIGS. 7-7E are highly enlarged diagrammatic views showingfloating seals according to alternate embodiments of the invention.

[0027]FIG. 8 is a schematic diagram showing a collection tank/pumpingsystem for use with the rotary joint of FIG. 1.

DETAILED DESCRIPTION

[0028] A rotary joint 10 is shown in FIG. 1. In FIG. 2, rotary joint 10is mounted on a bearing housing 6, which supports the journal 8 of acalendar roll 12, for example a calendar roll suitable for use inpapermaking. Rotary joint 10 includes an inlet conduit 14, through whicha fluid, e.g., hot oil, can enter the rotary joint, and an outletconduit 16, though which the fluid can exit the rotary joint. In use,these conduits are connected to a fluid supply, e.g., a source of hotoil (not shown). The fluid supply is configured to heat oil exiting therotary joint and pump it back into the rotary joint. The direction offlow of fluid through the rotary joint is indicated by the arrows inFIG. 2. The hot fluid flows from the inlet conduit through an internalsupply pipe 18 (FIG. 2) and thus into the calendar roll 12 to heat thesurface of the calendar roll. The fluid makes several passes (not shown)under the surface of the calendar roll, as is well known in thepapermaking field, and then exits the rotary joint via outlet conduit16.

[0029] The rotary joint 10 serves as an interface between the fluidsupply, which is stationary, and the rotating calendar roll. In FIG. 2C,rotating parts are cross-hatched and stationary parts are notcross-hatched, to facilitate understanding of which parts are rotatingand which are stationary. An inner portion 20 of the rotary jointrotates with the calendar roll, while an outer housing portion 22 of therotary joint remains stationary. The inner portion 20 includes aninternal supply pipe 18, and, joined to the internal supply pipe, afemale ring retainer 24 and an outer seal mating cylinder 26. Referringto FIG. 3, female ring retainer 24 defines an inner seal cavity 42. Theouter portion 22 includes an outer housing 28, an end cover 30 mountedon the outer housing, and inlet and outlet conduits 14, 16 extendingthrough the end cover. The outer portion also defines a leak drain hole31 and a normally closed vent hole 37 as well as a nitrogen inlet hole29. Vent hole 37 is provided for maintenance purposes, to allow air intothe roll when the system is being drained to minimize drain down timeand vapor lock.

[0030] It is necessary to seal between the rotating inner portion of thejoint and the stationary outer portion, to allow fluid to efficientlycycle in and out of the joint. Without seals, excessive amounts of fluidwould be lost, and fluid pressure through the roll could not be properlymaintained. However, we have found that it is not necessary tocompletely eliminate leakage. Instead, a controlled amount of leakagecan be allowed, and the leaking fluid can be collected and, if desired,recycled with the fluid that exits through outlet conduit 16 by the useof a separate collection tank/pumping system.

[0031] An example of a suitable collection tank/pumping system is shownin FIG. 8. In the embodiment shown in FIGS. 1-3, leaking fluid passesout of drain hole 31 (arrow L in FIG. 2A). As shown in FIG. 8, theleaking fluid passes through conduit 100 and is collected in a jointreturn tank 102. A return pump 104 pumps the fluid from the joint returntank 102, through a conduit 106 and back to the inlet conduit 14 of therotary joint via the suction of the calendar hot oil pump (not shown).As indicated in FIG. 8, a level valve 108 is provided to maintain aconstant level of liquid in the tank, to prevent the return pump fromdrawing in air should the tank become empty. Level valve 108 is governedby a level transmitter 110 and a level controller 112. Should the levelin the tank become too high, excess fluid will exit the joint returntank, via conduit 114 and flow into a hot oil storage tank (not shown).

[0032] An acceptable rate of leakage can be, for example, up to 5% ofthe total flow, typically from about 0.5-2% of the total flow.Preferably, the rate of leakage is sufficiently low so that the size andcost of the required collection tank and pumping system can beminimized. However, if desired, leakage may be adjusted to 10% of thetotal flow or more, simply by providing a pump large enough toaccommodate return of the leaking fluid to the rotary joint. The totalamount of acceptable leakage will vary depending on a number of factors,but in some applications may be, for example, from about 1 to 20gallons/minute.

[0033] Because some leakage is acceptable, it is not necessary to useleak-proof seals between the rotating and stationary portions of thejoint. Instead, floating seals can be used, allowing clearance andrelative axial and radial movement between the portions. The clearanceand radial motion accommodate movement of the bearing housing 6 (FIG.2A) and manufacturing tolerances, while the relative axial movementaccommodates thermal expansion and contraction of the parts as thecalendar roll and rotary joint are heated by the hot fluid.

[0034] Thus, referring to FIG. 3, the female ring retainer 24 carries afloating high-pressure seal assembly 32 that seals between the outerseal surface 33 of the inlet conduit 14 and the inner surface of thefemale ring retainer 24, reducing leakage of fluid in the directionindicated by arrow L in FIG. 3. Thus, seal 32 reduces leakage of fluidthat is flowing into the calendar roll (arrows F, FIG. 3). Thehigh-pressure seal 32 is effective at relatively high fluid pressures,e.g., 60 psi and greater. A pressure of 60 psi is typically exerted atfluid flow rates of 400-600 gallons/minute in the direction of arrows Fin FIG. 3. There is a large clearance area 42, e.g., about 0.05 to 0.06inches wide, between the outer diameter of the rings and the innersurface of female ring retainer 24, allowing the rings to “float” andproviding the clearance and axial/radial movement discussed above. Ifdesired, the clearance area may be significantly wider, e.g., 0.125 inchor more.

[0035] Seal 32 includes a plurality of coaxially arranged rings 34 thathave substantially the same inner and outer diameters. Rings 34 areshown in detail in FIGS. 5 and 5A and will be described below. Referringto FIG. 5A, each of the rings includes a relatively thick outer region36 and a relatively thin inner region 38 defining a land 41. Referringagain to FIG. 3, the rings are arranged so that the inner regions 38(see FIG. 5A) act as dams, and the difference in thickness betweenregions 36 and 38 defines a plurality of spaces 40 (FIG. 3) between therings that provide fluid turbulence zones. Because of clearance betweenland 41 and seal surface 33, a small amount of fluid can pass under theinner regions 38 and into spaces 40. Because the clearance is very smalland the rings are closely spaced, there is a rapid pressure drop andturbulence as fluid attempts to pass through the seal.

[0036] Thus, the liquid being sealed must pass between the narrow lands41 of the sealing rings and the seal surface 33. This clearance is verysmall (e.g., 0.003″-0.005″), minimizing the flow of the liquid. Theliquid slows as it enters the open area 40 before it flows through thenext land on the next ring. This creates microturbulence and a smallpressure drop at each ring interface (i.e., the interface between land41 and seal surface 33). When enough rings are stacked together theadditive pressure drop of each ring results in a small amount of leakagethrough the seal assembly. Thus, more rings can be added to reduceleakage if desired. Generally, the number of rings is only limited byspace constraints and cost. Similarly, if higher leakage can betolerated, fewer rings can be used.

[0037] At the end 44 of the seal at which leaking liquid enters, a wavespring 160 is positioned to bias the rings 34 towards the opposite end46 of the seal, pressing the rings together and resisting the pressureof the leaking fluid, which tends to force the rings apart. Because thewave spring exerts this biasing force, the wave spring further inhibitsflow of leaking fluid between the rings 34 and also around the rings inregion 42 because they are held against each other and against the sealretaining cover 61, effectively blocking that potential leakage path. Asuitable wave spring is shown in FIGS. 6 and 6A and discussed below.Like the rings, the wave spring is positioned to “float” in the sealedarea, with a clearance similar to that provided between the rings andinner flange.

[0038] Similarly, a seal-carrying portion 48 of the outer housing 28carries a low-pressure seal 50 that seals between the outer surface 52,of the outer cylinder 26, and the seal-carrying portion 48 of thehousing. Seal 50 reduces leakage of fluid in the direction indicated byarrow L_(R) in FIG. 3, and thus reduces leakage of fluid that isreturning from the calendar roll (arrows R, FIG. 3). Fluid that leakspast seal 50 leaks first into a chamber 77, from which it is directed bya rotating baffle 79 through opening 81 into a baffled and nitrogenpurged chamber 80 (FIG. 2A). Rotating baffle 79 prevents most or all ofthe leaking fluid from contacting wall 83 (the face of the journal). Thefunction of the nitrogen purge of chamber 80 will be discussed below.The low-pressure seal 50 is effective at moderate fluid pressures, e.g.,about 10 to 15 psi. These pressures are typically exerted at fluid flowrates of 400 to 600 gallons/minute in the direction of arrows R in FIG.3.

[0039] Like seal 32, seal 50 includes a wave spring that biases therings toward the end that is opposite the end at which fluid enters theseal. Thus, the wave spring 56 is positioned at end 58, to bias therings towards opposite end 60.

[0040] Referring to FIG. 2A, the liquid that leaks through seal 32 mixeswith the main body of liquid exiting the rotary joint, as indicated byarrows R, while the liquid that leaks through seal 50 exits the rotaryjoint through leak drain hole 31, as indicated by arrow L.

[0041] Because the floating seals are comprised of floating rings and afloating ring-shaped wave spring, the rotary joint can be easilyassembled by positioning the rings and spring in the area to be sealedand then bolting a cover in place. For example, referring to FIG. 3,cover 61 is provided for seal 32 and a cover 64 is provided for seal 50.The seals can be maintained and replaced, as needed, simply by removingthe cover and any rings that require repair or replacement.

[0042] As noted above, referring to FIGS. 2A and 2B, fluid that leakspast seal 50 leaks into a baffled and nitrogen purged chamber 80 of thehousing. Unlike adjacent chamber 82, chamber 80 is not flooded withfluid when the rotary joint is in use (see FIG. 2B, in which areascontaining fluid are shaded). As a result, if chamber 80 is not purgedwith nitrogen there is air present in the chamber. This air will tend tooxidize any leaking oil that enters chamber 80, potentially causingcoking and posing a fire risk if an ignition source is present. Thus, asdiscussed above it is desirable that chamber 80 be purged with nitrogenduring use of the rotary joint to prevent oxidation.

[0043] Referring to FIG. 2A and FIG. 4, the rotary joint 10 furtherincludes a nitrogen-conserving seal 62 that seals between the outerhousing 28 and the calendar roll journal 8. This seal inhibits leakageof nitrogen from chamber 80, thus minimizing the cost of providing thenitrogen purge. Seal 62 is similar in structure to the seals discussedabove, except that it includes fewer rings 84, because seal 62 only hasto seal at low pressures of about 0.5″ water (the pressure of thenitrogen in chamber 80). Like the seals discussed above, the rings arebiased by a wave spring 86 in the direction of fluid flow into the seal.

[0044] Referring to FIG. 2A, as a safety feature, a “tell-tale” openingTT is provided adjacent the seal 62 at the bottom of the rotary joint.If the chamber 80 were to become flooded with fluid, e.g., in the eventof a seal failure, liquid would flow out of the tell-tale. A sensor canbe positioned to detect and signal the presence of liquid flowing fromthe tell-tale, e.g., by sounding an alarm or providing an indication ona control panel. Alternatively, visual detection can be used todetermine if liquid is flowing from the tell-tale.

[0045] A ring suitable for use in the high-pressure floating sealdescribed above is shown in FIGS. 5 and 5A. As discussed above, ring 34includes a relatively thick outer region 36 and a relatively thin innerregion 38. Referring to FIG. 5A, typically the outer region 36 has athickness T₁ of from about 0.125 to 0.250 inch and a width W₁ of fromabout 0.125 to 0.250 inch, and the inner region 38 has a thickness T₂ offrom about 10-20% of T₁, and a width W₂ of from about 4 to 10 times T₂.Generally, the ratio of T₁ to T₂ is from about 1:10 to 1:5, and theratio of W₁ to W₂ is from about 1:1 to 2:1. The smaller the thicknessT₂, the greater the leakage control but also the greater the tendencyfor land 41 to wear relatively quickly. For a rotary joint to be usedwith a calendar roll having a diameter of 52 inches, typically the innerdiameter ID of ring 34 is from about 4.0 to 5.0 inches, and the outerdiameter OD is from about 4.5 to 5.5 inches.

[0046] Rings suitable for use in the low-pressure floating seal andnitrogen-conserving seal are similar to the ring shown in FIGS. 5 and5A. The low-pressure seal rings 54 and nitrogen seal rings 84 typicallyhave similar dimensions for T₁, W₁, T₂, and W₂. For a rotary joint to beused with a calendar roll having a diameter of 52 inches, typically theinner diameter ID of the low-pressure seal rings is from about 9 to 10inches, and the outer diameter OD is from about 9.5 to 10.5 inches,while the inner diameter ID of the nitrogen seal rings is from about 17to 18 inches, and the outer diameter OD is from about 17.5 to 18.5inches.

[0047] Because there is relative motion between the lands 41 of thesealing rings and the opposed sealing surfaces 33 and 52 of the high andlow pressure seals, the lands will tend to wear during use, which willeventually increase leakage through the seals. If desired, the sealsurfaces 33 and 52 may be electroplated with nickel to increase themetal lubricity and thereby reduce the wear rate of this criticalclearance area.

[0048] A suitable wave spring for use in biasing the rings is shown inFIGS. 6 and 6A. Wave spring 56 includes waves 70 (FIG. 6A), and a freegap 72, as is well known in the art. When wave spring 56 is compressed,waves 70 are flattened and free gap 72 is reduced or closed. In itscompressed position, wave spring 56 exerts a biasing force that isdetermined by the material of the spring and the free height and workheight of the waves (FIG. 6A). The properties of the wave springs usedin the high pressure, low pressure and nitrogen-conserving seals aregenerally similar, but can differ if desired. The free inside diameterand free outside diameter of the wave spring are generally substantiallythe same as the OD and ID of the rings used in the seal. The forceexerted by the wave spring may be adjusted by using more than one wavespring (stacking them coaxially), and/or by selecting a wave spring withdesired properties. If too little pressure is exerted by the wavespring(s), the rings may tend to move axially which may result inincreased leakage through the seal. If too much pressure is exerted bythe wave spring(s), the lands of the rings may wear at an undesirablyhigh rate.

[0049] Preferably, the entire rotary joint is formed of the samematerial, to minimize differences in thermal expansion between the partsof the joint and minimize changes in clearance between the parts duringthermal cycling. Generally, it is preferred that the rotary joint beformed of steel for durability, strength and ease of manufacture.

[0050] It is also preferred that the rotary joint include a centeringjack 88, as shown in FIG. 4, for aligning the housing of the rotaryjoint to the journal when a self-aligning spherical roller-bearing isused to support the rotation of the calendar roll.

[0051] Other embodiments are within the scope of the following claims.

[0052] The floating seal may have many other ring configurations. Forexample, as shown in FIG. 7, in a seal 120 rings 122 are arranged sothat their lands 124 face in alternating, opposite directions, toprovide a tortuous path through which the leaking fluid can flow. Otheralternative configurations are shown in FIGS. 7A-7E. As shown in FIG.7A, a seal 130 may include rings 126 that are substantially rectangularin cross-section, without a narrow region 38. As shown in FIG. 7B, inseal 140 similar rings 128 include lands 132 that are radiused to reducewear. As shown in FIG. 7C, a seal 150 may include rings 136 having apair of opposed relatively thin regions 138, defining a chamber 142. Asshown in FIG. 7D, a seal 160 may include rings 143 with pointed sealingedges 144. The pointed sealing edges may result in a progressivelyreduced wear rate for rings 143, due to increased land area as thepointed edges wear down. As shown in FIG. 7E, a seal 170 may includerings 146 that are biased on an angle to increase shear of the fluidleaking under the sealing lands. This configuration may be beneficialwhen the fluid to be sealed is relatively viscous, e.g., adhesives orresins.

[0053] The rotary joint is also self-venting. As is well known in theart, upon system start-ups it is necessary to vent a large volume of air(e.g., a 300 gallon volume or more) that has been introduced into theroll or oil system as a result of draining all the oil out during ashut-down. The floating seals of the rotary joint described above allowthe air to vacate the liquid loop very quickly through the seal rings.This self-venting feature minimizes pump cavatation when first startingthe system up from a maintenance outage, reducing down-time and laborcosts. For example, a volume of about 300 gallons can typically ventthrough the rotary joint described above in less than about 3 minutes.

[0054] Moreover, while the rotary joint discussed above is suitable fordelivering hot oil to a calendar roll, the rotary joint can be used inother applications, to join any desired rotating and stationary members.For example, the rotary joint can be used in applications that involvecontinuous heating or curing of a sheet material, e.g., with laminatingrolls used in the textile industry and with other types of nip rolls.The liquid delivered can be cold, to chill the rotating member, and maybe any desired liquid. If the liquid is corrosive, the rotary joint maybe formed of stainless steel, titanium, or other inert material.

[0055] Moreover, instead of wave springs, any other desired type ofbiasing device may be used, including coil springs and leaf springs.

What is claimed is:
 1. A rotary joint configured to couple a rotatingmember to a relatively stationary member, comprising a housing,configured to fit over the rotating member and receive a fluid to bedelivered from the stationary member to the rotating member; a rotatablecoupling disposed within the housing, configured to be fixedly attachedto the rotating member; and a floating seal system configured to allow acontrolled amount of fluid to leak from the rotary joint during deliveryof a fluid from the stationary member to the rotating member.
 2. Therotary joint of claim 1 wherein the controlled amount is from about 0.5to 2.0% of the total flow of fluid into the rotary joint.
 3. The rotaryjoint of claim 2 wherein the controlled amount is from about 1 to20gallons/minute.
 4. The rotary joint of claim 1 wherein the rotatingmember comprises a calendar roll.
 5. The rotary joint of claim 1 whereinthe floating seal system comprises a plurality of floating labyrinthseals.
 6. The rotary joint of claim 5 wherein said floating labyrinthseals are disposed between the rotatable coupling and portions of thehousing.
 7. The rotary joint of claim 1 further comprising anitrogen-purged chamber configured to capture the fluid leaking from therotary joint and allow this fluid to be collected for return to therotary joint.
 8. The rotary joint of claim 1 wherein the rotary jointdoes not include bearings.
 9. The rotary joint of claim 1 wherein therotary joint does not include mechanical seals.
 10. The rotary joint ofclaim 1 wherein the housing and rotatable coupling are formed of thesame material.
 11. The rotary joint of claim 10 wherein the material issteel.
 12. The rotary joint of claim 1 wherein the floating seal systemis configured to allow air to self-vent through the rotary joint uponstart-up after a maintenance outage.
 13. The rotary joint of claim 12wherein the floating seal system is configured to allow air to ventthrough the rotary joint at a rate of at least 25 gallons/minute. 14.The rotary joint of claim 13 wherein the floating seal system isconfigured to allow air to vent through the rotary joint at a rate of atleast 100 gallons/minute.
 15. A rotary joint configured to couple arotating member to a relatively stationary member, comprising a housing,configured to fit over the rotating member; an end plate, extending froma distal end of the housing and configured to allow the stationarymember to be fixedly attached to the housing; a rotatable couplingdisposed within the housing, configured to be fixedly attached to therotating member, and to receive a portion of the end plate in sealingengagement; a first seal, configured to provide sealing engagementbetween the rotatable coupling and the portion of the end plate, and asecond seal, configured to provide sealing engagement between therotatable coupling and an inner wall of the housing.
 16. The rotaryjoint of claim 15, further comprising a third seal, configured toprovide sealing engagement between a rotatable roll journal and theinner wall of the housing.
 17. The rotary joint of claim 15 wherein saidfirst and second seals are floating seals.
 18. The rotary joint of claim16 wherein said first, second and third seals are floating seals. 19.The rotary joint of claim 15 wherein said first and second sealscomprise floating labyrinth seals.
 20. The rotary joint of claim 15wherein the rotary joint does not include bearings.
 21. The rotary jointof claim 15 wherein the rotary joint does not include mechanical seals.22. The rotary joint of claim 15 wherein the housing and rotatablecoupling are formed of the same material.
 23. The rotary joint of claim22 wherein the material is steel.
 24. The rotary joint of claim 15wherein said first seal is a high-pressure seal.
 25. The rotary joint ofclaim 15 wherein said second seal is a low-pressure seal.
 26. The rotaryjoint of claim 16 wherein said third seal is a purge gas-conservingseal.
 27. The rotary joint of claim 15 wherein said rotatable couplingincludes a second portion configured for insertion into a cavity in therotating member.
 28. The rotary joint of claim 15 wherein the stationarymember is configured to deliver a fluid to the rotating member throughthe rotary joint.
 29. The rotary joint of claim 27 wherein said secondportion of said rotatable coupling sealingly engages said portion ofsaid end plate, the sealing engagement being provided by said firstseal.
 30. The rotary joint of claim 27 wherein said second portion ofsaid rotatable coupling and said portion of said end plate define abore.
 31. The rotary joint of claim 30 wherein said end plate defines aninlet, and said bore is configured to allow fluid flow from said inletto a cavity in the rotating member.
 32. The rotary joint of claim 31wherein said end plate further defines an outlet, and an outer wall ofsaid second portion of said rotatable coupling and an inner wall of acavity in the housing define a passage through which fluid can flow fromsaid rotating member to said outlet.
 33. A method of delivering fluidfrom a stationary source to a rotating member, comprising delivering afluid from the source to a rotary joint comprising a housing, configuredto fit over the rotating member and having a portion configured toreceive the fluid; passing fluid through a rotatable coupling, disposedwithin the housing and configured to be fixedly attached to the rotatingmember; and allowing a controlled amount of fluid to leak past afloating seal system disposed between the rotatable coupling and thehousing.
 34. The method of claim 33 wherein the controlled amount isfrom about 0.5 to 2.0% of the total flow of liquid into the rotaryjoint.
 35. The method of claim 34 wherein the controlled amount is fromabout 1 to 20 gallons/minute.
 36. The method of claim 33 wherein thefloating seal system comprises a plurality of floating labyrinth seals.37. The method of claim 33 further comprising collecting the leakedfluid and returning it to the source for delivery into the rotary joint.38. The method of claim 33 wherein the liquid is hot oil.
 39. The methodof claim 38 wherein the liquid is mineral oil.
 40. The method of claim38 further comprising purging air-containing areas of the housing withan inert gas to inhibit oxidation of the oil.
 41. The method of claim 33wherein the liquid has a viscosity lower than that of water when theliquid is being circulated near its fluid maximum bulk operatingtemperature.
 42. The method of claim 33 further comprising purgingair-containing areas of the housing.
 43. A floating seal for sealingbetween an inner cylindrical surface and an outer cylindrical surface,the inner and outer surfaces defining a chamber, the seal comprising: aplurality of rings configured to fit in the chamber, positionedside-by-side along the length of the chamber, and to float within thechamber; and a biasing member configured to apply an axial end pressureto the rings in the direction of fluid entering the chamber during useof the seal, keeping the rings compressed together and against an endface of the chamber to minimize leakage around the outside diameter ofthe rings.
 44. The floating seal of claim 43 wherein the chamber thatcontains the rings is at least 0.100 inch larger in diameter than theouter diameter of the rings.
 45. The floating seal of claim 44 whereinthe chamber is from 0.100 to 1.00 inch larger in diameter than the outerdiameter of the rings.
 46. The floating seal of claim 43 wherein thebiasing member comprises a wave spring.
 47. The floating seal of claim43 wherein said floating seal is configured to minimize leakage of aliquid through the seal.
 48. The floating seal of claim 43 wherein therings are configured to provide a tortuous path comprising alternatingrestricted areas and larger turbulence-creating void areas.
 49. Afloating seal for sealing between an inner cylindrical surface and anouter cylindrical surface, the inner and outer surfaces defining achamber, the seal comprising a plurality of rings configured to define atortuous path comprising alternating restricted areas and largerturbulence-creating void areas.
 50. A rotary joint configured to couplea rotating member to a relatively stationary member, comprising ahousing, configured to fit over the rotating member and receive a fluidto be delivered from the stationary member to the rotating member; arotatable coupling disposed within the housing, configured to be fixedlyattached to the rotating member; and a floating seal system comprising afloating labyrinth seal including a plurality of rings configured todefine a tortuous path comprising alternating restricted areas andlarger turbulence-creating void areas.